Such a method and apparatus are already known in the art, e.g. from the European Patent Application 94114620.1 "Method for temporal filtering of video signals using a motion adaptive spatial filter". In this document a motion-adaptive spatial filtering method and apparatus are presented, performing part of front-end processing on a video signal which needs to be encoded afterwards. The involved filtering steps serve to eliminate or to alleviate temporal noises and perform band limitation to thereby improve picture quality and encoding efficiency. The purpose of temporal filtering is to remove noise components in moving areas of successive frames, without affecting the details therein.
The filtered signal is then further encoded using e.g. standard MPEG-2 encoding techniques. This encoding method first identifies so-called reference frames in the video stream to be encoded, applies an intracoding algorithm to these reference frames, and further encodes the other frames differentially with respect to these reference frames. Even with the mentioned prior art front-end processing, the resulting bitstream after MPEG-2 encoding remains very bursty, resulting in a high peak-to-mean bitrate ratio of the encoded updated video stream. This high peak-to-mean bitrate ratio creates a serious problem for transmitting these encoded data using ATM transfer capabilities. This problem could be alleviated by over-dimensioning the ATM-network, or by using a flattening MPEG transport stream, in which the encoded updated video elementary stream is packetised into a packet elementary stream, and further integrated into a transport stream consisting of fixed length packets. This solution results in an inefficient use of the network, since a lot of these fixed length packets will contain useless bits.